Modern tuning devices, such as those used in set top boxes to receive satellite transmissions, often have multiple tuners. The use of multiple tuners permits a set top box to perform several functions that would otherwise be difficult or impossible. For example, a multi-tuner set top box may display a picture-in-picture output or may record one program while another is sent from the set top box for display on a display device.
Multi-tuner set top boxes typically employ band stacking and translation to process multiple signals originating from multiple sources, such as two or more satellite transmitters. Briefly, band stacking is the process of placing two discrete signal bands on a single cable. The discrete signals occupy different frequencies of the input and are often separated by a guard zone, which is a frequency band containing no signal data. Band translation is the operation of combining band stacked signals into one or more outputs and may include, for example frequency mixing and/or frequency translating of one or more signals.
For example, if a set top box has two tuners, it may receive signals from two separate satellites. Each satellite generally transmits a left-hand circular polarized signal and a right-hand circular polarized signal. Thus, if a set top box has two tuners, it may receive four signals—two from each satellite. The two signals from each satellite may be band stacked into a single input signal, thus yielding two input signals in total (one for each satellite). These band stacked signals may then be translated to yield two different stacked outputs. The first stacked output may contain, for example, the left-hand circular polarized feed from each of the first and second satellites while the second stacked output may contain the right-hand circular polarized feed from each of the satellites. Band stacking and band translation are more thoroughly described in U.S. patent application Ser. No. 11/256,472, filed Oct. 20, 2005; and U.S. patent application Ser. No. 11/140,330, filed May 27, 2005, both naming Edmund F. Petruzzelli as inventor.
The process of band stacking generally requires a relatively high-frequency signal produced by a local oscillator in a low noise block converter feedhorn (“LNBF”) of a customer's receiving system. However, accurate high-frequency local oscillators can be expensive. Further, it is more difficult to produce an accurate high-frequency local oscillator than a low-frequency local oscillator, and high-frequency local oscillators may have a shorter service life. Accordingly, there is a need in the art for an improved low noise block converter feedhorn.